Choose all of the correct answers for each of the following: the relations of tw

Question

Choose all of the correct answers for each of the following: the relations of two sub-entity sets of the same super entity set have the same keys the same attributes the same constraints the same natural joins with their super entity set All of the above None of the above the condition A = B in a WHERE clause of an SQL query, where A is an attribute in relation R and B an attribute in relations S. is true for all values of A and B where A = B for all values of A and B where A = B except when A has a NULL value for all values of A and B where A = B except when B has a NULL value for all values of A and B where A = B except when A and B have NULL values All of the above None of the above the condition A

Explanation / Answer

A) None of the above

Because the sub-entity may don't have same keys, attributes, constraints as super entity

Ex: Super Entity { AB->C, B->D, CD->E}

Sub-Entity { B->D} // This won't contains same keys, attributes, constraints as Super entity

B) Answer is 4.

Because NULL=NULL is undefined in SQL

C) Answer is 1 & 4.

Because NULL should not be compared with a value. because the result is unpredictable/true

D) Answer is 2
Because s should not be compared to a NULL, which results are unpredictable and depends on vendor

E) Answer is 2 & 4

Because when attribute A in Relation R is changed then it's existence is checked against attribute B in Relation S. Similarly if the attribute B is changed then it is informed that there are dependants on this.

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